This invention relates to a shredding apparatus for shredding unnecessary sheets, e.g., unnecessary documents, drawings, films, etc., into fine chips.
The shredding apparatus commonly termed shredder can desirably shred unnecessary sheets into as fine chips as possible. This is so because the finer the produced chips are, the more it is difficult to reproduce the record on the shredded sheets, that is, the more convenient it is to keep the record confidential.
Japanese Utility Model Disclosure No. 58-119,845 discloses a shredder which can shred unnecessary sheets in their longitudinal and lateral directions into fine chips. The shredder disclosed has a plurality of pairs of rotary cutting disks, with the rotary cutting disks of each pair being rotated in opposite directions as they come together. As the rotary cutting disks of the individual pairs are rotated in opposite directions, unnecessary sheets are cut in the direction, in which the sheets are fed into the shredder. Each rotary cutting disk has a plurality of teeth formed in a spaced-apart relationship to one another and at a uniform spacing on its outer periphery, the teeth each having an axial or lateral edge serving as a blade. The shredder also has back plates each having a back surface, which is substantially complementary in contour to and extends around and in a close proximity relation to the "addendum" surface of the associated rotary cutting disk. Thus, with the rotation of the individual rotary cutting disks their teeth cut the unnecessary sheets in the lateral direction thereof, i.e., in the direction perpendicular to the direction in which the sheets are fed, in co-operation with the back surfaces of their associated back plates. The rotary cutting disks further each have radial projections formed on the periphery between adjacent teeth. These radial projections serve to prevent the produced chips from being caught between axially adjacent rotary cutting disks.
The prior art shredder as described above has the following drawbacks. With the rotation of the pairs of rotary cutting disks, the unnecessary sheets being fed or supplied thereto are withdrawn into between two rows of rotary cutting disks in a shredding arrangement with each other to be shredded therebetween. The withdrawal of the supplied sheets are chiefly effected by the teeth of the individual rotary cutting disks. However, since the teeth are formed in a spaced-apart relationship around the circumference of the rotary cutting disks, with withdrawal forces acting on the sheets are produced intermittently. Therefore, it is liable that the sheets fail to be withdrawn smoothly, with the result that the sheets are shredded not smoothly but roughly and unsatisfactorily. This difficiency is particularly pronounced in case when a large number of sheets are withdrawn at a time.
The intermittent withdrawal of sheets given rise to another drawback that a pulsating load is applied to the drive shafts of the rotary cutting disks, this increasing the burden on a drive motor for driving the drive shafts.